1. Field of the Invention
The present invention relates to a process for forming sound images on a color photographic material and, more particularly, to a process for forming an optical sound track on a multilayer color photographic material.
2. Description of the Prior Art
In general, there are two types of processes for recording sound images on a color photographic material for use in the field of motion pictures or television: one is an optical sound-recording system and the other is a magnet sound-recording system. The present invention relates to a process for forming sound tracks suitable for use in the optical sound-recording system.
The reproduction of sound by an optical sound-recording system in a color print film, a color reversal film, a color reversal print film, etc. as is used in the field of motion pictures or television is accomplished by the steps of converting a sound signal recorded on a film as a variation in density or area to a light signal, converting the light signal to an electrical signal by means of a light acceptor and then converting the electrical signal to a sound signal. In such reproduction steps, photoelectric tubes having various spectral characteristics are used as a light acceptor. Of these, the one used most universally is designated S-1 type, which has a spectral sensitivity maximum in the infrared region at about 800 m.mu. (see, for example, Adrin Cornwell Clyne, Color Cinematography, page 593 (1951)).
On the other hand, in conventional color photographic materials based on a subtractive color process, the main absorption of the dyes formed by the coupling reaction between an oxidation product of a color developing agent, such as a p-phenylenediamine, and a color coupler is always in a region of the visible spectrum, which absorption therefore does not coincide with the spectral characteristics of the abovedescribed photoelectric tube. These color dye images provide, therefore, a sound output which is too weak to be practical. Consequently, in recording sound on a color photographic material, usually a processing step which forms silver images or silver sulfide on a sound track is carried out, and the density in the infrared region of the thus obtained silver images or silver sulfide images is utilized for the reproduction of sound. The infrared density (transmitting density) of these silver or silver sulfide images ranges generally from 1.0 to 0.6.
The production of sound tracks on a color print film can be carried out by using the procedures as described in, for example, Journal of the Society of Motion Picture and Television Engineers, vol. 77, page 1154 (1968).
According to these procedures, color images in picture areas and sound images in sound track areas are color-developed at the same time in a color developing bath. In a first fixing bath, unexposed silver halide is removed and, in a bleaching bath, developed silver produced by the developing step is rehalogenated. In the sound developing step, silver halide only in the sound track areas is converted to a silver image by selectively applying a viscous sound developer solution to the sound track areas. In a second fixing bath, the silver halide in the picture areas is fixed and removed and, in a stabilizing bath, the image dyes are stabilized. The density in the infrared region of the silver images thus formed on a sound track is predominantly utilized for the reproduction of sound.
Therefore, in the production of sound tracks in a color film, the step for forming the silver images or the silver sulfide images is indispensable as described above. The reason for forming a sound track comprising silver or silver sulfide is, as described above, because the photoelectric tube which is employed in the process of sound reproduction has its maximum sensitivity in the infrared region, while in such region of the spectrum the density of color dyes formed by color developing step is insufficiently low. Accordingly, the step to produce silver images or silver sulfide images in the sound track area is needed in addition to the step of forming dye images in the picture area.
Recently, methods to produce sound tracks without such a step have been provided. For example, as described in U.S. Pat. applications Ser. Nos. 439,675, filed Feb. 4, 1974, 451,658, filed Mar. 15, 1974 and U.S. Pat. Nos. 3,705,801, 3,715,208, and 3,737,312, a color photographic light-sensitive material which comprises an auxiliary layer containing a compound which is capable of protecting the sound image from the effect of a bleaching agent and restraining silver bleaching (a silver bleach inhibitor) is provided. When using a light-sensitive material as described, it is possible to form sound images simply by conventional color processing without conducting the so-called sound development. However, these light-sensitive materials having such an auxiliary layer containing a silver bleach inhibitor entail certain disadvantages. That is, due to the formation of the auxiliary layer (the sound track forming layer) in addition to the conventional image forming layers, the sensitivity of the image forming layers which are positioned under the sound track forming layer is reduced and the sharpness of the images decreases markedly. For example, when the sound track forming layer is formed in the farthest position from the support (uppermost position), the frequency modulation property of the sound images is improved but the sharpness of picture images decreases. On the contrary, when the sound track forming layer is located closest to the support, the sharpness of the picture images formed in the image forming layers over the sound track forming layer is not affected but good frequency modulation properties cannot be obtained. This is a great difficulty in the practical use of these color photographic light-sensitive materials having such an auxiliary sound track forming layer.
Another method of forming sound tracks without a sound developing step is described in Japanese Pat. application Laid Open No. 24431/74 and U.S. Pat. No. 3,705,800, in which a multilayer color photographic light-sensitive material is developed to form a picture record comprising silver and a dye and a sound track record comprising silver and then a silver bleach inhibitor is selectively applied to the silver of the sound track record. in Japanese Pat. application Laid Open No. 24431/74, the disclosure is that a compound having at least two oxyalkylene groups or a compound having at least one mercapto group can be suitably used as the silver bleach inhibitor. According to the method described in Japanese Pat. application Laid Open No. 24431/74, after development of a multilayer color photographic light-sensitive material, the silver bleach inhibitor as mentioned above is applied to only the sound track area containing silver to protect the silver sound track record from the action of the silver bleaching agent, and then the material is treated in a single bleach-fixing bath. Although a shortening of the overall processing time can be achieved by treating in such a bleach-fixing bath, this method is accompanied by the following disadvantage. That is, in order to recover silver from a treating bath for a color photographic light-sensitive material, in particular a motion picture film, a method of electrolyzing the fixing solution is generally and preferably used. The method is described, for example, in Journal of the Society of Motion Picture and Television Engineers, vol. 81, pages 603-608. However, when such a single bleach-fixing bath as described in Japanese Patent Application Laid Open No. 24431/74, German Pat. Nos. 866,605 and 966,410, and British Journal of Photography, pages 122-123 and 126 (1966) is employed, the silver recovery by electrolysis is difficult to perform due to the presence of other metal ions than a silver ion such as an iron ion in the solution.
Also Japanese Pat. application Laid Open No. 13483/72 describes a method for preparing a sound track which comprises developing a multi-layer color photographic light-sensitive material, contacting the sound track area containing silver with a silver bleach inhibitor having a mercapto group or a seleno group, and carrying out the bleaching step. According to the method, the silver bleach inhibiting action may be enhanced by using an onium salt such as a quaternary ammonium compound, a quaternary phosphonium compound or a tertiary sulfonium compound together with the silver bleach inhibitor having a mercapto group or a seleno group, however, the description is that these onium salts are not silver bleach inhibitors within the meaning of the term as defined therein.